The present invention relates to a liquid crystal display apparatus and a backlight adjustment method.
A liquid crystal display (hereinafter abbreviated as an LCD), which is of non-self emitting type, needs backlight as a light source. Examples of the backlight are a cold cathode ray tube and a light emitting diode (hereinafter abbreviated as an LED). When an LED is used, a white diode can be used. However, in a liquid crystal television monitor, three-primary color LEDs of R (red), G (green), and B (blue) are often used to improve color reproducibility. By mixing these colors of these LEDs, white backlight is formed.
When a white LED is used for backlight, since the luminance and chromaticity of the backlight depend on the current that flows in the LED, the duty of on time and off time of the current that flows in the LED is controlled as disclosed in related art (Japanese Patent Laid-Open Publication No. 2002-324685).
In the related art as shown in FIG. 16, the luminance of backlight for an LCD module is adjusted by controlling current, duty, and so forth. In other words, an output current value of an LED drive current source 11 is controlled by a current value control circuit 12. A switch circuit 14 is disposed between the LED drive current source 11 and a white LED 15. The switch circuit 14 is turned on/off with a PWM signal of a PWM generation circuit 13. The duty ratio of the PWM signal is controlled with a control signal supplied from a duty ratio control circuit 16. However, the luminance of the backlight of the LCD module described in the document deteriorates by aged deterioration or the like.
In the past, when an LCD module was shipped, the luminance of the backlight was adjusted. The luminance of the backlight was controlled by a thermistor as a temperature detection device. Alternatively, the end user needed to adjust the luminance of the backlight.
Thus, after the liquid crystal display had been shipped, the aged deterioration of the luminance of the backlight could not be handled or it was improperly adjusted. Thus, the user needed to adjust the luminance of the backlight.